Liquid fuels and oils often become contaminated with water when ambient water, such as from condensation formed within a vented storage tank, is mixed with the fuel/oil. This may give rise to a liquid mixture comprising separate, visible phases of fuel/oil and water, thus rendering the liquid fuel/oil unsuitable for application. This problem is particularly significant with fuels or oils stored over a long period of time. Where a fuel or oil is contained within a storage tank which is vented to the atmosphere, ambient temperature changes, such as between day and night, can act to effectively pump atmospheric air, containing water vapour, in and out of a head space above the stored fuel/oil. Over a number of temperature change cycles, for example over a number of hot days and cold nights, such pumping, combined with condensation of the water vapour, can give rise to the accumulation of water within the tank which may exist as a separate phase within the fuel/oil. The removal of water formed in the fuel tank of a powered water craft left unattended over a winter period is a known problem. Further, besides potentially rendering a fuel/oil unsuitable for use, such as in a combustion process, the presence of such accumulated water may provide an environment for the growth of micoorganisms, such as bacteria, funghi, protazoa and the like. Such growth may give rise to formation of a sludge in a stored fuel/oil and thus also render it unsuitable for normal use. The removal of a sludge from a fuel/oil storage tank is known to be a very significant problem in the bulk storage of liquid fuels/oils, such as on a tank farm associated with an oil refinery.
It is an object of the present invention to protect a liquid fuel or oil from contamination by water, which contamination may give rise to a two phase fuel/oil and water mixture and/or to the growth of microorganisms.
It is another object of the present invention to render suitable for application a liquid fuel or oil which has become contaminated with water.
The use of water as an additive in fuel oils to reduce emissions of pollutants and to aid incorporation of other beneficial performance additives has been known for many years. The use of water as an additive in lubricant oils to improve the cooling properties of e.g. cutting oils has also been known for many years. Water is incorporated into the fuel and lubricant oils in the form of a water-in-oil emulsion.
Water-in-oil emulsions formed with a large water droplet size tend to have a milky appearance. These emulsions require a number of secondary additives such as corrosion inhibitors and bactericides to overcome problems associated with addition of the water phase. These macroemulsions, due to their large water droplet size, also tend to exhibit instability that leads to oil/water separation. Naturally, this is unwelcome as it may lead to problems with not only machine failure but also problems with ignition e.g. in a diesel-engine.
Cutting oils, based on water-in-oil emulsions, have been used to lubricate machine tools. The excellent coolant property of the water has been demonstrated to improve the life of the tool. However, the incorporation of water coupled with the instability of macroemulsions give rise to other problems, such as the lubricity of the oil, which is decreased with addition of water thereby affecting the surface finish of the metal.
Water-in-oil emulsions formed with an average water droplet size of less than 0.1 μm (hereafter referred to as “microemulsions”) are translucent. This small droplet size not only gives an appearance which is more aesthetically pleasing to the user but also offers several major advantages over the larger droplet-sized systems. These translucent or clear microemulsions tend to be more stable than the larger droplet sized milky macroemulsions, as the water droplets remain in dispersion longer and do not readily undergo macro oil/water phase separation. The small droplet size also appears to negate the need for both corrosion inhibitors and bactericides.
U.S. Pat. No. 3,095,286 (Andress et al) discloses the problem of water accumulation in fuel oil storage tanks, resulting from the “breathing” of storage vessels, presenting a problem of rusting. To inhibit sedimentation, screen clogging and rusting in fuel oil compositions during storage it is disclosed to use a compound selected from a phthalamic acid, a tetrahydrophthalamic acid, a hexahydrophthalamic acid and a nadamic acid and their salts of primary amines having between 4 and 30 carbon atoms per molecule as an addition agent to the fuel oil. There is no disclosure of the addition agents forming water-in-oil microemulsions of the fuel oil.
U.S. Pat. No. 3,346,494 (Robbins et al) discloses the preparation of microemulsions employing a selected combination of three microemulsifiers, specifically a fatty acid, an amino alcohol and an alkyl phenol.
FR-A-2373328 (Grangette et al) discloses the preparation of microemulsions of oil and salt water by employing sulphur containing surfactants.
U.S. Pat. No. 3,876,391 (McCoy et al) discloses a process for preparing clear, stable water-in-petroleum microemulsions, which may contain increased quantities of water-soluble additives. The microemulsions are formed by use of both a gasoline-soluble surfactant and a water-soluble surfactant. The only water-soluble surfactants employed in the worked examples are ethoxylated nonylphenols.
U.S. Pat. No. 4,619,967 (Emerson et al) discloses the use of water-in-oil emulsions for emulsion polymerisation processes.
U.S. Pat. No. 4,770,670 (Hazbun et al) discloses stable water-in-fuel microemulsions employing a cosurfactant combination of a phenyl alcohol and an ionic or nonionic surfactant.
U.S. Pat. No. 4,832,868 (Schmid et al) discloses surfactant mixtures useful in the preparation of oil-in-water emulsions. There is no disclosure of any water-in-oil microemulsion comprising at least 60 wt % oil phase.
U.S. Pat. No. 5,633,220 (Cawiezel) discloses the preparation of a water-in-oil emulsion fracturing fluid including an emulsifying agent sold by ICI under the trademark Hypermer (Hypermer emulsifying agents are not disclosed as being C6-C15 alcohol ethoxylates or mixtures thereof).
Mixtures of C6-C15 alcohol ethoxylates are commercially available surfactants normally sold for use in the preparation of e.g. washing detergents.
WO-A-9818884 discloses water-in-fuel microemulsions, including examples of such emulsions comprising a C8 alcohol ethoxylate, with 6 EO groups, mixed with a polyglyceryl-4-monooleate, and mixtures of C9-C11 alcohol ethoxylates mixed with either polyglyceryl oleates linear alcohols or POE sorbitan alcohols. The presence of the polyglyceryl oleates and POE sorbitan alcohols tend to have detrimental effects on the viscosity properties of the emulsions which, in turn, has a consequential detrimental effect on the lubricity properties of the emulsion.
WO-A-9850139 discloses a water-in-oil microemulsion, including a surfactant mixture comprising a fatty acid amine ethoxylate, a C6-C15 alcohol ethoxylate and optionally a tall oil fatty acid amine. The water-in-oil microemulsion may be an industrial lubricant.
WO-A-0053699 discloses a water-in-oil microemulsion, including emulsifying agents comprising a C6-C15 alcohol ethoxylate, an amine ethoxylate and a polyisobutylsuccininide or sorbitan ester. The water-in-oil microemulsion may be a fuel.
EP-A-1101815 discloses a fuel, particularly for diesel engines, in microemulsion form, comprising a liquid fuel, an emulsifier and an emulsive agent, the emulsive agent having an HLB value higher than 9.
U.S. Pat. No. 6,716,801 discloses a stable, clear water-in-oil microemulsion consisting of from about 5 to 40 wt % aqueous phase and from about 95 to about 60 wt % non-aqueous phase. The microemulsion includes from about 5 to 30 wt % emulsifiers consisting of i) a mixture of C6-C15 alcohol ethoxylates each comprising from 2 to 12 EO groups, ii) 0 to about 25 wt % polyisobutylsuccinimide and/or sorbitan ester, and iii) 0 to about 90 wt % amine ethoxylate. The microemulsion is described to be useful as a fuel and/or lubricant/coolant.
The water-in-oil emulsions previously sold for use as fuels and lubricants generally contain surfactants that, due to incomplete combustion, form combustion by-products that are potentially harmful to the environment, such as nitrogen-, phenyl- and sulphur-containing compounds, and/or have detrimental effects on the lubricity properties. There is a continuing need therefore to provide new and/or improved fuels and lubricants that do not suffer the same problems. With this background, however, any new fuel and lubricant must also perform at least as well as the prior art fuels and lubricants. The prior art microemulsions overcome at least some of the problems associated with water-in-oil emulsion and demonstrate good performance properties. However, there is a continuing demand for microemulsions which are able to deliver good performance properties as well as overcoming the problems associated with water-in-oil emulsions.
It is another object of the present invention to provide water-in-oil microemulsions that may be used as fuels and/or lubricants and which, without loss of performance, employ surfactants that may be more environmentally acceptable than those hitherto employed in fuels. It is a further object of the present invention to provide a novel water-in-oil microemulsion that may require less surfactant than is used in conventional water-in-oil microemulsion fuels and lubricants.
As there is a tendency in the design of modern engines to employ the fuel not only as a fuel per se, but also as a lubricant and coolant, such as where a portion of fuel is continually recirculated between the hot engine and fuel tank, it is a further object of the present invention to provide a water-in-oil microemulsion fuel or lubricant that may demonstrate improved stability, such as thermal stability.
It is a further object of the present invention to provide a water-in-oil microemulsion fuel or lubricant that may demonstrate improved lubricity.